This module add spin transfer torque term proposed by Z. Li and S. Zhang
(Phys.Rev.Lett.\textbf{93}(2004) pp.127204).
\begin{equation}
	\Gamma_{STT} =
	b_j\overrightarrow{m}\wedge\left(\overrightarrow{m}\wedge\frac{\partial\overrightarrow{m}}{\partial\overrightarrow{j}_e}\right)
	- c_j\overrightarrow{m}\wedge\left(\frac{\partial\overrightarrow{m}}{\partial\overrightarrow{j}_e}\right)
\end{equation}
With:
\begin{eqnarray}
	b_j&=&\frac{\mu_BP\left|\left|\overrightarrow{j_e}\right|\right|}{eM_s\left(1+\xi^2\right)}\\
	c_j&=&\xi\frac{\mu_BP\left|\left|\overrightarrow{j_e}\right|\right|}{eM_s\left(1+\xi^2\right)}
\end{eqnarray}
$\mathrm{\mu_B}$ is Bohr magneton.\\
e is the charge of the electron\\
$\mathrm{M_S}$ is the saturation magnetisation\\
$\mathrm{\xi}$ is the rate of adiabaticity\\
$\mathrm{\overrightarrow{m}}$ is the mqgnetisation normalised\\
$\mathrm{\overrightarrow{j}_e}$ is the electronic current density\\
P is the polarisation rate\\